Resistance element for a non-linear potentiometer



June 13, 1967 H. B. CASEY 3,325,763

RESISTANCE ELEMENT FOR A NON-LINEAR POTENTIOMETER Filed Dec. 2, 1964 woo OUTPl/Ib VOLZS' INVENTO/F HARRY 8. CASE) ATTORNEY United States Patent Ofiice 3,325,763 Patented June 13, 1967 3,325,763 RESISTANCE ELEMENT FOR A. NON-LINEAR PGTENTIOMETER Harry B. Casey, Willow Grove, Pa., assignor to IRC, Inc., a corporation of Delaware Filed Dec. 2, 1964, Ser. No. 415,426 9 Claims. (Cl. 338--3tl9) The present invention relates to a non-linear potentiometer, and more particularly to a potentiometer which provides a sine or cosine voltage function. Even more particularly, the present invention relates to a film type resistance element for a potentiometer which provides a sine and cosine voltage function.

Heretofore, a sine or cosine voltage function was achieved in a potentiometer by means of either a resistance element comprising a resistance wire wound on a properly shaped card or by means of a special mechanical linkage between the actuating shaft and the movable contact of the potentiometer. However, each of these techniques for achieving such a non-linear function require a rather complex structure so that the resulting potentiometer is relatively expensive to manufacture. Also, these complex structures are relatively large in size which has become undesirable with the recent trend in the electronics industry toward miniaturization.

It is therefore an object of the present invention to provide a novel resistance element for a potentiometer which provides a non-linear voltage function.

It is another object of the present invention to provide a novel resistance element for a potentiometer which provides a sine and cosine voltage function.

It is still another object of the present invention to provide a film type resistance element for a potentiometer which provides a sine and cosine voltage function.

It is a further object of the present invention to provide a film type resistance element for a potentiometer which provides a sine and cosine voltage function and which can be made in small sizes for miniaturized otentiometers.

It is a still further object of the present invention to provide a film type resistance element for a potentiometer which provides a sine and cosine voltage function and which is of simple construction so that it can be easily and inexpensively manufactured.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a top plan view of a potentiometer resistance element of the present invention.

FIGURE 2 is a sectional view taken along line 22 of FIGURE 1.

FIGURE 3 is a top plan view of a modification of the potentiometer resistance element of the present invention.

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 3.

FIGURE 5 is a diagram of the function achieved by the resistance element of the present invention.

In general, the resistance element of the present invention comprises a fiat plate of an electrical insulating material, such as a plastic or ceramic, having a narrow terminating strip of an electrically conductive metal coated on one surface thereof. A film of an electrical resistance material is coated on said one surface of the flat plate and extends from the terminating strip. The resistance film has a first portion of a width which progressively increases from a minimum at the terminating strip to a maximum at a point spaced from the terminating strip and a second portion extending beyond said point and of a uniform width equal to the maximum width of the first portion. A film of an electrically conductive metal is coated on said one surface of the flat plate in overlapping and contacting relation with the second portion of the resisttance film. The electrically conductive metal film is so shaped that the amount of overlap between the metal film and the resistance film progressively increases from adjacent the junction between the two portions of the resistance film to the other end of the second portion. As will be explained in detail later, the rate of increase of the Width of the first portion of the resistance film provides an increase in the resistance value of the resistance film from the terminating strip according to the sine function and the progressively increasing amount of overlap between the metal film and the second portion of the resistance film provides a continuing increase of the resistance value according to the sine function from the maximum resistance end of the first portion. This achieves a resistance element which will provide one-quarter of a cycle of a sine and cosine function. As will be explained in more detail, additional portions of the cycle of the sine and cosine function can be obtained by extending the resistance film and the electrically conductive metal film with the extension being shaped as a mirror image of the resistance film and metal film described above.

Referring initially to FIGURES 1 and 2, the potentiometer resistance element of the present invention is generally designated as 10.

Resistance element 10 comprises an annular, flat plate 12 of an electrical insulating material, such as a plastic or ceramic. A pair of narrow terminating strips 14a and 14b of an electrically conductive metal, such as silver, are coated on a surface of the plate 12 and extend along a common diameter of the plate. A film 16 of an electrical resistance material is coated on the surface of the plate 12 and extends across the terminating strips 14a and 14b. The film 16 may be of any of the well known resistance materials and is of a form to provide the desired sine and cosine function shown in FIGURE 5. As can be seen from FIGURE 5, the form of one-half of the cycle of the sine and cosine function is identical to the form of the other one-half except as to polarity. Thus, to achieve this function, the form of one-half of the path of travel of the resistance film 16 can be identical to the form of the other one-half. Also, it can be seen that the form of each one quarter of the cycle is identical. Therefore, the form of one-quarter, a degree segment, of the resistance film 16 will be described since such segment is then repeated for the other three segments.

In the 90 degree segment of the resistance film 16, the resistance value must follow the equation R=R sine 0 where R=the resistance value at any given point, 0=the angle of displacement of the point from the beginning of the segment, and R =the total resistance value of the 90 degree segment of the resistance film. From this equation and the diagram shown in FIGURE 5 it can be seen that starting at zero degrees, the resistance value of the re sistance film must increase at a decreasing rate along the 90 degree segment.

Although the desired function can be achieved by a resistance film which is of a desired minimum width at zero degrees and which progressively increases in width at an increasing rate, this form of the resistance film is not practical since the film becomes too wide to fit on the insulating plate 12. I have found that the desired function can be obtained with a resistance film composed of a first portion which is of a desired minimum width at Zero degrees and which progressively increases in width in accordance with the sine function until the width of the film equals the width of the insulating plate 12, and a second portion which is of a Width equal to the width of the insulating plate 12 and which extends from the widest end of the first portion to the 90 degree point on the insulating plate. To continue the sine function over the second portion of the resistance film, a film of electrically conductive metal, such as silver, is provided over a part of the second portion of the resistance film. The conductive film extends from a point adjacent the end of the first portion of .the resistance film and is of progressively increasing width toward the 90 degree point.

Referring again to FIGURE 1, and considering the terminating strip 14a as the Zero degree point, the width of the resistance film 16 at the .terminating strip 14a is shown as being approximately one-half the width of the plate 12. Moving clockwise around the plate 12, the width of the resistance film 16 progressively increases to provide increasing resistance values according to the previously stated formula. It has been found that at approximately the 65 degree point, the width of the resistance film 16 is equal to the width of the plate 12. From the 65 degree point to the 90 degree point, the width of the resistance film 16 is uniformly the width of the plate 12. Films 18a and 20a of an electrically conductive metal are provided over a part of the resistance film 16 between a point adjacent the 65 degree point and the 90 degree point. Co-nductive film 18a extends along the outer periphery of the plate 12, and the conductive film 20a extends along the inner periphery of the plate 12. The widths of the conductive films 18a and 20a progressively increase from adjacent the 65 degree point to the 90 degree point. The conductive films 18a and 20a are electrically connected by a strip 21a of the conductive metal extending radially along the 90 degree point.

From the 90 degree point to the terminating strip 14b, the resistance film 16 and the conductive films 18a and 20a are shaped as the mirror images of the portions of the resistance film and conductive films between the terminating strip 14a and the 90 degree point. Over the other half of the plate 12, the shape of the resistance film 16 is identical to the shape of the resistance film over the first half of the plate. At the 270 degree point conductive films 18b and 20b are provided over the resistance film 16 which are identical in shape to the conductive films 18a and 20a at the 90 degree point. The conductive films 18b and 20b are electrically connected by a strip 21b.

In use, the resistance element is placed in a potentiometer casing having fixed terminals for the resistance film, a movable contact and means for moving the movable contact along the resistance film. For example, the resistance element 10 can be mounted in the casing of the variable resistor shown in United States Patent No. 3,096,- 499, issued July 2, 1963 to M. W. Hudson et al., entitled, Variable Resistor, or in the casing shown in United States Patent No. 2,908,882, issued Oct. 13, 1959, to H. A. Gottschall et al. entitled, Potentiometer, or in any other Well known potentiometer casing. The terminating strips 14a and 14b of the resistance element 10 are connected to a fixed terminal of the potentiometer casing which is grounded. The conductive films 18a and a of the resistance element 10 are electrically connected through a fixed terminal of the casing to the positive side of a source of electrical current, and the conductive films 18b and 20b are electrically connected through a fixed terminal of the casing to the negative side of the source of current.

Starting with the movable contact engaging the resistance film 16 at the point over the terminating strip 14a, the voltage output across the resistance element 10 is zero since the terminating strip 14a is grounded. As the movable contact is moved along the resistance film 16 clockwise, the votlage output across the resistance element increases positively according to the sine function because of the increasing width of the resistance film until the 65 degree point is reached. From the 65 degree point to the 90 degree point, the movable contact passes between conductive films 18a and 20a. Along this portion of the resistance film 16, the voltage output continues to increase at a decreasing rate according to the sine function because the movable contact becomes electrically closer to the degree point through the conductive films 18a and 20a. When the movable contact reaches the 90 degree point, the voltage output is at its maximum on the positive side. As the movable contact moves along the resistance film 16 from the 90 degree point toward the terminating strip 14b, the voltage output decreases according to the sine function until zero voltage is again reached at the terminating strip 14b which is grounded. Movement of the movable contact along the other half of the resistance film 16 from the terminating strip 14b back to the terminating strip 14a produces the negative portion of the sine function. Thus, movement of the movable contact along one revolution of the resistance film 16 produces one complete cycle of the sine function.

Although the conductive films 18a, 18b, 26a and 20b, 21a and 21b are shown as being coated overthe resistance film 16, the conductive films may be coated directly on the surface of the plate 12 with the resistance film being coated over the conductive films. Also, instead of having two separate conductive films at each of the 90 degree point and 270 degree point, a properly shaped single conductive film at each of these points can be used to achieve the same result. However, the use of two conductive films at each of these points is preferred so that there is provided a circular path along the resistance film 16 midway between the edges of the plate 12 along which the movable contact can easily travel. Although the conductive films 18a and 20a have been described as starting at the 65 degree point, the conductive films can start either before or beyond the 65 degree point. For example, if the width of the resistance film 16 at the terminating strip 14a, the zero degree point, is less than one-half the width of the plate 12, the width of the resistance film will not equal the width of the disk until it reaches a point beyond the 65 degree point. However, if thewidth of the resistance film at the zero degree point is greater than one-half the width of the plate 12, the width of the resistance film will equal the width of the disk at a point before the 65 degree point. Thus, according to the present invention, the conductive films 18a and 20a start at the point adjacent that at which the width of the resistance film 16 equals the width of the plate 12. The shapes of the conductive films 18a and 20a will vary slightly according to their starting points so as to provide the desired sine function. Thus, there is provided a film type resistance element which provides one complete cycle of a sine and cosine voltage function and which can be made in small sizes for miniaturized potentiometers.

The resistance element 10 of the present invention shown in FIGURES 1 and 2 provides a sine and cosine voltage function for a potentiometer having a movable contact which moves in a circular path. Referring to FIGURES 3 and 4, there is shown a resistance element of the present invention, generally designated as 30, which provides a sine and cosine voltage function for a potentiometer having a linear moving contact.

Resistance element 30 comprises a thin, fiat, rectangular plate 32 of an electrical insulating material, such as a plastic or ceramic. Plate 32 is of a length much greater than its width. A narrow termination strip 34 of an electrically conductive metal, such as silver, is coated on a surface of the plate 32 and extends across the width of the plate intermediate the ends thereof. A film 36 of a resistance material is coated on the surface of plate 32 and extends across the terminating strip 34. The portions of the resistance film 36 on each side of the terminating strip 34 are of identical shape and are mirror images of each other. The resistance film 36 is of minimum width at the terminating strip 34. From the terminating strip 34, the resistance film 36 progressively increases in width toward each end of the plate 32 according to the sine function formula previously stated with regard to the resistance element 10 of FIGURES 1 and 2 until the width of the resistance fihn equals the width of the plate 32. The width of the resistance film is then uniformly the same as the width of the plate 32 to the ends of the plate. At each end of the plate 32 a pair of films 38 and 40 of an electrically conductive metal, such as silver, are provided either over or under the resistance film 36 with each of the conductive films 38 and 40 extending along an opposite edge of the plate 32. The conductive films 38 and 40 are of progressively increasing width towards the ends of the plate 32 from a point adjacent the point that the resistance film reaches its maximum width. The conductive films 38 and 40 are shaped so that the width of the exposed part of the resistance film therebetween progressively decreases to provide a decreasing rate of increase of the resistance value according to the previously stated sine function formula. Each pair of the conductive films 38 and 40 are electrically connected by a conductive strip 42 extending across the end of the plate 32.

In use, the resistance element 30 is placed in a rectangular shaped potentiometer casing having fixed terminals and a moving contact which is adapted to move 'linearly through the casing. For example, the resistance element 30 can be mounted in the casing of the variable resistor shown in United States Patent No. 2,706,230, issued Apr. 12, 1955 to M. E. Bourns et al., entitled, Variable Resistor, or in the potentiometer casing shown in United States Patent No. 2,922,977, issued Jan. 26, 1960 to H. A. Gottschall, entitled, Rectilinear Potentiometer, or in any other similar type potentiometer casing. The terminating strip 34 of the resistance element 30 'is connected to a fixed terminal of the potentiometer casing which is grounded. The conductive films 38 and 40 at one end of the resistance element, for example the conductive films at the left-hand end as viewed in FIG- URE 3, are electrically connected through a fixed terminal to the positive side of a source of electrical current. The conductive films 38 and 40 at the other end of the resistance element are electrically connected through a fixed terminal to the negative side of the source of electrical current.

Starting with the movable contact engaging the resistance film 36 at the point over the terminating strip 34, the voltage output of' the resistance element 30 is zero since the terminating strip 34 is grounded. As the movable contact is moved along the resistance film 36 toward the left-hand end of the resistance element 30, the voltage output of the resistance element increases positively according to the sine function first because of the increasing width of the resistance film and finally because of the shape of the conductive films 38 and 48. At the left-hand end of the resistance element 30, the maximum voltage output is obtained. The movable contact is then moved back along the resistance film 36 toward the terminating strip 34 to complete the positive half of the sine function. Movement of the movable contact from the terminating strip 34 to the right-hand end of the resistance element 30 and back to the terminating strip provides the negative half of the since function. Thus, the resistance element 30 provides one complete cycle of the sine voltage function upon linear movement of the movable contact along the resistance film 36.

Although the potentiometer resistance element of the present invention has been described as being constructed to provide a sine and cosine voltage function, it should be understood that the construction described herein can provide other voltage functions. There are many functions of voltage which can be achieved with a potentiometer having a resistance path of varying width along its length. However, in providing such voltage functions with a miniature potentiometer the problem often arises of being able to fit the resistance path of the base plate. Using the resistance element construction of the present invention, such voltage functions can be achieved by varying the width of the first portion of the resistance path according to the desired function until the resistance path is of a width equal to the width of the base plate. The remaining portion of the resistance path is of uniform width and an electrically conductive film extends over the second portion of the resistance path and is shaped to provide a continuation of the desired voltage function. The electrically conductive film is connected to the source of electrical current so as to provide a voltage across the length of the resistance path.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A potentiometer resistance element adapted to provide a sine and cosine voltage function comprising a fiat plate of an electrical insulating material, a narrow terminating strip of an electrically conductive metal coated on a flat surface of said plate, a film of an electrical resistance material coated on said surface of the plate and contacting said terminating strip, said resistance film having a first portion of a width which progressively increases from a minimum at the terminating strip to a maximum at a point spaced from the terminating strip and a second portion extending beyond said point and of a uniform width equal to said maximum width, the rate of increase of the width of said first portion of the resistance film providing an increase in resistance value of the resistance film from the terminating strip according to the sine function, and a film of an electrically conductive metal coated on said plate in overlapping and contacting relation with the second portion of the resistance film, the amount of overlap between said conductive film and the resistance film progressively increasing from the said point so that the resistance value of said resistance film continues to increase according to the sine function from said point to a maximum resistance value.

2. A potentiometer resistance element in accordance with claim 1 in which the flat surface of the plate has one dimension considerably greater than its other dimension, the terminating strip extends along the smaller dimension of the surface, and the resistance film extends along the greater dimension of the surface.

3. A potentiometer resistance element adapted to provide a sine and cosine voltage function comprising a fiat annular plate of an electrical insulating material, a narrow terminating strip of an electrically conductive metal coated on and extending radially across a fiat surface of said plate, a film of an electrical resistance material coated on said surface of said plate and extending from said terminating strip to a point degrees spaced therefrom, said resistance film having a first portion the width of which at the terminating strip is less than the width of the plate and which progressively increases in width from said terminating strip to the width of the plate at a point spaced from the 90 degree point, and a second portion extending beyond said first portion to said 90 degree point and of a uniform width equal to the width of the plate, the rate of increase of the width of said first portion of the resistance film providing an increase in resistance value of the resistance film from the terminating strip according to the sine function, and a film of an electrically conductive metal coated on said plate in overlapping and contacting relation with the second portion of the resistance film, the amount of overlap between said conductive film and the resistance film progressively increasing from the junction of said portions of the resistance film to the 90 degree point so that the resistance value of said resistance film continues to increase according to the sine function from said junction to a maximum resistance value at the 90 degree point.

4, A potentiometer resistance element in accordance with claim 3 in which the conductive film comprises two spaced portions, one of said two portions extending along tends from the first terminating strip to the the outer edge of the plate and the other of said two portions extending along the inner edge of the plate, and a third portion extending between and electrically connecting said two port-ions at the 90 degree point.

5. A potentiometer resistance element in accordance with claim 4 including a second narrow terminating strip of an electrically conductive metal coated on and extending radially across the said surface of the plate at a point 180 degrees from the first terminating strip, and the first mentioned resistance and conductive film extend over the surface of the plate between the 90 degree point and the second terminating strip, and are shaped as the mirror image of the shape of the resistance and conductive films between the first terminating strip and the 90 degree point.

6. A potentiometer resistance element in accordance with claim 5 in which the resistance film extends over the surface of the plate around the entire circumference of the plate, the shape of the part of the resistance film which extends from the second terminating strip back to the first terminating strip being substantially identical to the shape of the part of the resistance film which exsecond terminating strip, and a second film of an electrically conductive metal coated on said plate and overlapping the resistance film at and adjacent to a point 180 degrees spaced from the first conductive film, said second conductive film being shaped substantially identical to the shape of said first conductive film.

7. A potentiometer resistance element adapted to provide a sine and cosine voltage function comprising a fiat rectangular plate of an electrical insulating material, the length of said plate being substantially greater than the width of the plate, a narrow terminating strip of an electrically conductive metal coated on a flat surface of said plate and extending across the width of said plate midmay between the ends of the plate, a film of an electrical resistance material coated on said surface of the plate and extending from said terminating strip to one end of the plate, said resistance film having a first portionthe width of which at the terminating strip is les than thewidth of the plate and which progressively increases in width from said terminating strip to the width of the plate at a point spaced from said one end of the plate, and a second por- Q 0 tion extending beyond said first portion to said one end of the plate and of a uniform width equal to the width of the plate, the rate of increase of the width of said first portion of the resistance film providing an increase in resistance value of the resistance film from the terminating strip according to the sine function, and a film of an electrically conductive metalcoated on said plate in overlapping and contacting relation with the second portion of the resistance film, the amount of overlap between said conductive film and the resistance film progressively increasing from the junction of the portions of the resistance film to said one end of the plate so that the resistance value of said resistance film continues to increase according to the sine function from said junction to a maximum resistance value at the said one end of the plate.

8. A potentiometer resistance element in accordance with claim 7 in which the conductive film comprises two spaced portions, each of said two portions extending along an opposite edge of said plate .and a third portion extending between and electrically connecting said two portions and said one end of the plate.

9. A potentiometer resistance element in accordance with claim 8 in which the resistance film extends beyond the terminating strip to the other end of the plate, the shape of the resistance film between the terminating strip and the other end of the plate being the mirror image of the shape of the resistance film between the terminating strip and the one end of the plate, and a second film of an electrically conductive metal coated on said plate in overlapping and contacting relation with the resistance film at the other end of the plate, the shape of said second conductive film being the mirror image of the shape of the first said conductive film.

References Cited UNITED STATES PATENTS 2,457,178 12/1948 Richardson et al. 33890 X 2,820,873 1/1958 Klestadt 33889 3,184,694 4/1965 Weinschel 338142 X RICHARD M. WOOD, Primary Examiner.

I. G. SMITH, Assistant Examiner. 

7. A POTENTIOMETER RESISTANCE ELEMENT ADAPTED TO PROVIDE A SINE AND COSINE VOLTAGE FUNCTION COMPRISING A FLAT RECTANGULAR PLATE OF AN ELECTRICAL INSULATING MATERIAL, THE LENGTH OF SAID PLATE BEING SUBSTANTIALLY GREATER THAN THE WIDTH OF THE PLATE, A NARROW TERMINATING STRIP OF AN ELECTRICALLY CONDUCTIVE METAL COATED ON A FLAT SURFACE OF SAID PLATE AND EXTENDING ACROSS THE WIDTH OF SAID PLATE MIDMAY BETWEEN THE ENDS OF THE PLATE, A FILM OF AN ELECTRICAL RESISTANCE MATERIAL COATED ON SAID SURFACE OF THE PLATE AND EXTENDING FROM SAID TERMINATING STRIP TO ONE END OF THE PLATE, SAID RESISTANCE FILM HAVING A FIRST PORTION THE WIDTH OF WHICH AT THE TERMINATING STRIP IS LESS THAN THE WIDTH OF THE PLATE AND WHICH PROGRESSIVELY INCREASES IN WIDTH FROM SAID TERMINATING STRIP TO THE WIDTH OF THE PLATE AT A POINT SPACED FROM SAID ONE END OF THE PLATE, AND A SECOND PORTION EXTENDING BEYOND SAID FIRST PORTION TO SAID ONE END OF THE PLATE AND OF A UNIFORM WIDTH EQUAL TO THE WIDTH 